Traditionally, muscle building exercise has been associated with the lifting of free weights, which are simply plates of steel, or cement filled plastic, positioned on a bar which resist a force applied by a user through the action of gravity. Such free-weight exercise apparatus provide a consistent resisting force, due to the consistent nature of gravity, therefore providing the same resistance to the user applied force throughout the range of motion of the exercise. For example, in the case of exercising the biceps of the upper arm, the user stands up straight, grasping the bar with an equally distributed weight on either side with his hands, and brings the bar upward against the resisting force of gravity, by bending his arms at the elbows to thereby provide a strain to the biceps muscle group.
Typically, each time the user performs this range of motion it is called a repetition or rep. By performing a plurality of reps, the biceps group of muscles in both arms of the user is fatigued, causing slight shredding of the muscle tissue which becomes stronger and more massive upon healing. In addition, the user will generally perform a variety of other exercises using the free-weight system. Such exercises include the bench press, in which the user lies on a bench and presses the free-weight system in a motion reciprocating the bar from his chest, where his arms are most bent, to a position where his arms are substantially straightened.
Also, the user may perform the seated shoulder press in which he sits upright on a bench and presses the free-weight system up over his head in a range of motion from where the bar is resting on his shoulders behind his head, at a position where his arms are most bent, upwards to a position where his arms are substantially straightened. A similar mode of exercise may be performed by resting the bar of the free-weight system in front of his head towards his chest and pressing upward. Another weight lifting exercise is called a triceps curl, which is substantially the reverse of the biceps curl, wherein the force resisting the user applied force is resisting the motion of the user's arms to fatigue the triceps muscle groups.
In addition to the free-weight form of exercise, other exercise apparatus are designed to replicate other particular conventional exercise modes. Examples of these exercises include rowing, in which the user rows a stationary rowing machine, which replicates the rowing of a boat on water. Another example is the stationary exercise bicycle, in which an apparatus resembling a bicycle is pedaled by the user but remains stationary. In these forms of exercise, there is always applied a force to counteract the force applied by the user, and to cause the necessary muscle fatigue desired to complete the particular exercise.
Typically, there are four modes of exercise which a user may perform. Each mode has certain advantages and disadvantages over the others with regard to body conditioning, muscle toning, muscular bulking, endurance etc. These four modes of exercises may be called isometric, isotonic, isokinetic, and cardiovascular.
Isometric exercise is associated with an exercise in which a user applied force results in no range of motion. An example of this type of exercise is the simple act of placing the palms of the hands together and pushing one hand against the other, causing the muscles in the chest and arm to attempt to contract. This form of exercise may be advantageous over the other forms of exercise because of the very limited range of motion, and the static forces applied to the joints and associated tissue.
Isotonic exercise is associated with the mode of exercise in which the resistive force remains constant. An example of such an exercise is the above described free-weight lifting exercises. In isotonic exercise, the resistive force (i.e. the force of gravity) remains constant while the velocity of movement may vary along the range of motion. Isokinetic exercise is an exercise associated with a variable force resisting a user applied force along the range of motion of an exercise, so that the velocity along the range of motion of the exercise remains constant.
Cardiovascular exercise is associated with an exercise in which the heart and blood vessel system, as well as other muscle, organ and nervous systems of the body, are caused to experience consistent and relatively prolonged stress. A simple example of such an exercise is jogging. When one jogs, the arms and legs are constantly in motion propelling the jogger forward. Throughout the jog, the heart rate is elevated to supply nutrients and oxygen to the fatiguing muscles. This form of exercise, when done correctly, has many advantages over the other exercises, particularly with regard to overall health conditioning.
There have been attempts in the past to provide an apparatus which is multi-configurable so as to enable the performance of a variety of exercises. However, consistent with these attempts has been the construction of a device which replicates only one or two of the above described exercise modes. Most common of these conventional attempts, are devices which replicate the exercise mode associated with free-weight lifting. To replicate the resistive force of the free-weight system, these devices typically include elastic members which the user stretches during a particular exercise's range of motion, air piston systems which resist the user's applied force by absorbing the force through the compression of air filled in a chamber (using a piston and rod system), or devices which use steel plates which are restricted to movement along tracks. These devices have a variety of inadequacies.
Among the inadequacies of these above mentioned devices, the resistance to the user-applied force remains constant throughout the range of motion of a particular exercise. For example, when replicating biceps curls, the same force is applied to resist the user applied force regardless of whether the arms are at the beginning of a rep such as when in the out-stretched position, or at the end of a rep such as when in the bent-arm position, and the same resistive force is applied along the entire range therebetween.
However, the human body has various points along such a range of motion where the strength of a particular muscle group varies. For example, in the biceps curl range of motion the point of maximum muscular strength of the biceps group may be at a position located somewhere between the two ends of the range of motion, and the points of weakest strength of the particular muscle group may be at points at either end of the range of motion.
Thus, it is recognized that the prior art exercise devices which attempt to replicate the free-weight weight training system are failures because, like the free-weight system, they do not providing for compensation of this inconsistent muscle group strength along a particular range of motion. Also, there are dangers associated with such systems, due to, for example, discrepancy in muscular strength along the range of motion, excessive muscle fatigue and over exertion.
Typically, a user will over exert the muscle group at its weakest points in the range of motion which may seriously damage the body's tissue. Also, because the exercise motion is limited by the weakest points of the muscle group during a particular range of motion, the strongest points of the range of motion receive inadequate stress to maximize the positive effects of the exercise.
Further attempts in exercise devices have led to the construction of devices which may provide a variable resistance to a user-applied force along the range of motion of a particular exercise. Such a device typically requires the input of a counter-acting resistive force using an electric drive motor. A clutch system transmits this rotational force to resist a user applied force. This configuration is particularly inadequate, since the electric drive motor requires much power to be an effective source of resistance. Also, such a configuration is very complicated and prone to failure due to the fact that rotational force supplied by the motor must be coupled through a clutch mechanism to be used to resist the input of the user. There have been attempts to vary the resistance applied to counteract the user applied resistance over the exercise range of motion. These attempts are generally inadequate because, for example, they typically resist the force applied by the user in one-direction only. For example, in the case of the biceps curl these devices resist the user-applied force only in the upstroke, or the power stroke of the biceps group, of the exercise's range of motion. However, to maximize the exercise performed during a particular range of motion, such as the biceps curl exercise, it is desirable that the user-applied force is also resisted during the downstroke, or triceps muscle group power stroke.
Conventionally, the construction of a device capable of resisting the user-applied force, in both the upstroke and downstroke, of the biceps/triceps exercise range of motion, requires a very complicated and very expensive device. In addition, prior attempts to provide such an exercise apparatus failed to take into account the fact that, for example, the biceps group has a much stronger power stroke relative to the triceps group, resulting in inadequately designed devices.